1. Field of the Invention
The present invention relates to an apparatus and a method for determining a property of a thermal head including a plurality of heating devices.
2. Description of the Related Art
A thermal line printer (hereinafter referred to as a xe2x80x9cthermal printerxe2x80x9d) that is conventionally known uses, for example, a thermal head having a plurality of heating resistors linearly arranged to thermally record pictures, characters and the like on thermal paper of predetermined size. The thermal printer is composed of such main components as a printer engine PE including a thermal head and a paper feeder and a printer controller PC2 for controlling a printing process.
As shown in FIG. 4, for example, the printer engine PE is comprised of a thermal head 1, a motor 2 of a paper feed mechanism, and a sensor 3 for detecting the position of the thermal head. There are various model types of printer engines PE, and respective model types (or models) have different properties such as the rated voltage of the thermal head, the resistance of each heating resistor, the number of dots, and the number of driver ICs (that is, the number of blocks) for controlling current-carrying through the heating resistor or the like. Accordingly, the printer controller for controlling each of the different printer engines is provided with a control table which stores control information used for controlling each model optimally. Based on the control information depending on the printer engine to be controlled, the printer controller performs the control, thereby being capable of making the printer controller be commonly used.
The printer controller PC2 is provided with a CPU 10 for controlling the entire printer engine PE, a RAM 11 for storing various control constants, a ROM 12 for storing the control tables dedicated to each of the various models of printer engines PE, and a model setting switch 13 typically composed of a DIP switch and the like for setting a specific model of printer engine PE. By selecting the setting of the model setting switch 13, the printer controller PC2 can be adapted to a plurality of models of printer engines.
Furthermore, the printer controller PC2 includes a voltage measuring circuit 14 for carrying out a measurement of a power supply voltage which is supplied to the printer controller PC2 and the printer engine PE by an external power supply device 20, and a head configuration measuring circuit 15 for carrying out a measurement of the configuration of the thermal head 1 of the printer engine PE. The head configuration measuring circuit 15 measures specifically the resistance of each heating resistor, the number of dots, the number of blocks or the like of the thermal head 1.
Note that, the printer engine PE is detachably connected with the printer controller PC2 via a predetermined connector.
Incidentally, when the conventional printer controller PC2 is connected to the printer engine PE, the above-described model setting switch 13 has to be manually operated to make the setting suitable for the printer engine PE to be connected. Therefore, there is a problem that it is inconvenient in an assembly process in a plant or in a user""s replacement of the thermal head.
Furthermore, there is another problem that the inaccurate setting of the model setting switch 13 induces a breakage of the printer engine PE or a mis-action (error) of the printer engine PE, resulting in a failure in normal printing. In particular, when the printer controller PC2 performs an initial diagnostic process of the thermal head immediately after power-up, in the case where the model setting switch 13 is not set normally, the printer engine PE includes a fear that some errors occur to result in a failure of printing. The reason will be described below.
In the procedure shown in the flowchart of FIG. 5, the conventional printer controller PC2 performs an initial diagnostic process. First, the printer controller PC2 reads the setting of model setting switch 13 on power-up at step S100 and the process advances to step S101. The printer controller PC2 reads the control table for the set model from the ROM 12 at step S101, and it stores the control table into the RAM 11 as a memory for control at step S102, and thereafter the process advances to step S103. In the case where the model setting switch 13 is not accurately set, the printer controller PC2 reads a control table which does not match the thermal head connected at step S101, and it stores an inaccurate control table into the RAM 11 at step S102.
The voltage measuring circuit 14 carries out a measurement of the voltage applied to the printer engine PE at step S103, and thereafter the process advances to step S104. At step S104, the printer controller PC2 compares the difference between the measured voltage and the content of setting in the model setting switch 13. When the voltage matches the content of setting, the process advances to step S106, and when the voltage does not match the content of setting, the printer controller PC2 performs an error process to display an error, output a notifying beep and the like at step S105.
However, as described above, in the case where the model setting switch 13 is inaccurately set, there arises a difference between the content of setting itself in the model setting switch 13 to be compared with the measured voltage and the property of the printer engine PE connected. Accordingly, the printer controller PC2 has a problem in that it is impossible to perform an accurate determination at step S104. That is, the printer controller PC2 includes such troubles that it performs the error process even in a state where the voltage primarily matches the setting, or in contrast, it keeps performing the process in spite of a state where the voltage does not match the setting.
Further, the head configuration measuring circuit 15 carries out a measurement of the configuration of the thermal head 1 (the number of dots or the number of blocks) at step S106, and the process advances to step S107. At step S107, the printer controller PC2 compares the difference between the measured configuration of the thermal head and the content of setting in the model setting switch 13. When the voltage does not match the content of setting, the printer controller PC2 performs an error process at step S108, and when it is determined that the voltage matches the content of setting, it completes the processing. However, as in the case of the previous step S104, when the model setting switch 13 is inaccurately set, similarly the printer controller PC2 has a problem in that it is impossible to perform an accurate determination at this step S107.
Therefore, when the model setting switch 13 is inaccurately set, the printer controller PC2 has a probability in that it cannot accurately perform the initial diagnostic process of the thermal head. In the worst case, there are such probabilities in that the printer engine is not entirely actuated due to the applied voltage which does not match the specification of the printer engine PE, or in that the printer engine inaccurately works because of the setting of the control table for the other models.
A DIP switch or the like composing the model setting switch 13 has a problem in the structure where the above-described mis-setting easily occurs. Furthermore, from the viewpoint of a reduction in the cost of the thermal printer, there is a request for reducing the number of components as many as possible by removing the model setting switch itself if possible.
The present invention has been devised for solving the above-described problems. An object of the present invention is to provide a determining apparatus and determining method for determining the model type of a thermal head in a thermal printer capable of automatically performing a determination of a thermal head model type without a model type setting switch.
The thermal head determining apparatus in accordance with the present invention, for achieving the above-described object, is a determining apparatus (printer controller PC) for determining the model type of a thermal head (1) from a plurality of different model types, each thermal head model type including a plurality of heating devices (heating resistor 1a), wherein the determining apparatus comprises a thermal head property storing device (ROM 33) for previously storing property data of the plurality of various models of thermal heads, thermal head property measuring devices (voltage measuring circuit 34, head configuration measuring circuit 35) for measuring properties of a thermal head connected to the determining apparatus, and thermal head model type determining devices (CPU 30 and a program for head initial diagnostic process) for determining the thermal head model type connected to the determining apparatus by comparing/checking the property measured by the thermal head property measuring devices with the data stored in the thermal head property storing device.
Therefore, by simply connecting the thermal head (printer engine) with the printer controller PC, the printer controller PC can automatically determine the correct model of thermal head. Since the printer controller PC can specify a control table suitable for the thermal head based on the result of the determination, for example, it can prevent such a situation where a breakage or a mis-action of the thermal head occurs due to the mis-setting of the thermal head model.
Furthermore, since the printer controller PC does not need to have a model setting switch, it can prevent the occurrence of human error in setting the model type and it can reduce the number of components of the printer, resulting in a reduction in the cost of the thermal printer.
The property data of the thermal head includes: the rated voltage; the resistance of each heating device; and the number of dots.
Further, the thermal head property measuring devices can be composed of an applied voltage measuring device for measuring the voltage applied to the thermal head to be connected. Accordingly, when comparing/checking the measured voltage with the rated voltage relating to the property data of the thermal head, the printer controller PC can determine the model of the thermal head.
Furthermore, the thermal head property measuring devices can be composed of a thermal head configuration measuring device for measuring the resistance of each heating device and the number of dots in the thermal head to be connected. Accordingly, when comparing/checking the measured resistance of each of the heating device or the measured number of dots in the thermal head with the property data of the thermal head, the printer controller PC can more accurately determine the model of the thermal head.
Further, the thermal head property storing device and the thermal head property measuring devices may be included in a controller for controlling the thermal head. Accordingly, in the initial diagnostic process of the thermal head which is performed in the controller immediately after power-up, the printer controller PC can determine the model of the thermal head and also set the appropriate control table based on the result of the determination.
Furthermore, another aspect of the invention is a determining method for determining the property of the thermal head including a plurality of heating devices, wherein the determining method comprises the steps of storing previously the property data of the plurality of various models of thermal heads, measuring the properties of thermal head at the time of conenction of the thermal head to the printer controller PC, comparing/checking the result of the measurement with the property data of the thermal heads, and determining the model of the connected thermal head. Accordingly, by simply connecting the thermal head with the printer controller PC, the printer controller PC can determine automatically the correct model of the thermal head. Since the printer controller PC can specify the control table suitable for the thermal head based on the result of the determination, it can prevent the situation where a breakage or a mis-action of the thermal head occurs due to the mis-setting of the thermal head model.